Perhaps the cheapest effective retaining wall solution is using steel universal column posts with treated timber sleepers placed between the steel posts. Such a wall is strong and if the sleepers to warp or rot, they can be easily replaced.
That said, such a wall, if constructed poorly, can be a horrible eye-sore. To avoid this, below are some tips on making sure your retaining wall is both effective and attractive.
Base and Height of Wall
First thing to consider is determining your base height and top of wall height. If your wall is near to your house, then you’ll want the base of the wall to be at least 1 inch below the eventual path level beside your house, such that your path or paved area can slope away from your house. Once this point is determined, the wall height can be estimated. It’s most convenient to determine wall heights in 200mm (approx 8 inch) levels, as this is the typical sleeper height.
Distance Between Posts (Centers)
Next determine the end points of the wall. Let’s say it’s 13.6 meters from one corner to the other. Use some math to work our how many bays would be required to get a post separation between 1.1 and 1.5 meters. In this case, 10 bays at 1.36m each would be a good solution. The wider the bay, the more warping of sleepers will be apparent in the future. Anything beyond 1.8m is risky as it can require replacing warped sleepers within a few months.
Hole Depth & Diameter
Next is hole depth and diameter. The hole should be at least as deep as the height of the steel that is above ground level. Hence, a 600mm high wall needs holes at least 600mm deep. The steel column should go down into the concrete about 90% of the depth of the hole. When the height is only 200mm, it’s best to make the hole at least 350mm. In weak sandy soils, you’ll need to go beyond these recommendations, while in hard stable ground, such as drilled rock, you can get away with lower depths. With diameter, 350mm holes should suffice for most walls under 1 meter if the ground is quite firm. Increase the diameter to 450mm and beyond in soft soils. Stainless Steel Posts
Getting a Straight Wall
The trick to this is using string-lines between star posts that are hammered into the ground at each end of the wall. One string line will mark the top front of the wall. This should be level in most cases. If you don’t have professional leveling tools, a good trick is to place an eye behind the string line, and look through it to the brickwork of a house or a level roof gutter line and adjust the string line until it is parallel to that line. If this isn’t available, get a small string hanging level and hand it in the middle of the line. You can measure from the house outside wall to each end of the string line to make sure your wall is parallel to the house too.